2017 21.4602739726027
2016 21.5251366120219
2015 21.3884931506849
2014 21.4330065359477
2013 22.0481012658228
2012 21.3521857923497
2011 21.2901369863014
2010 21.8567123287671
2009 21.3666666666667
2008 20.9803278688525
2007 21.4424528301887
2006 20.5107142857143
2005 21.4613698630137
2004 21.5728260869565
2003 NA
2002 21.3796825396825
2001 21.146301369863